1. Field of the Invention
This invention relates generally to shoes used in tracked vehicles such as crawler shovels and cranes, bulldozers and similar industrial and construction equipment and is more particularly directed at a shoe structure suitable for fabrication from sheet metal.
2. State of the Prior Art
The track shoes of the prior art were formed in a single piece by sandcasting methods using manganese or alloy steel. The individual track shoes were then joined by means of hinge joints between adjacent track shoes in a manner well known in the art. It was found that the manganese or alloy steel wears in use such that the bores through which the hinge pin extends become enlarged in diameter through abrasion and result in a loose joint between adjacent track shoes. In addition, the shear strength of the cast manganese steel is comparatively low and the shoes can fracture due to torsional forces acting on the shoes and hinge joints as the track travels over uneven, rocky terrain. It is therefore desirable to manufacture such track shoes of a harder metal which can be machined to a greater precision to make smooth, snugly fitting bores and thus product a better, smoother hinge joint between the track shoes that make up the flexible vehicle track.
It often occurs in use that the individual track shoes, as they travel over uneven terrain, are subject to torsional forces which cause the bores of the shoes through which pass the retaining pins linking adjacent shoes to become off-round and enlarged so that the retaining pin no longer fits snugly and the shoes become loosely attached to each other. The practice is to bore the shoes to a larger diameter so that the bores once again become truly cylindrical and properly aligned and then resort to an over-sized pin of greater diameter to snugly fit within the enlarged bores. In the alternative, sleeve bushings may be inserted into the enlarged bores and the original retaining pin reused. It has been found that precision drilling of out-of-round bores in manganese steel cast track shoes is difficult and costly. By using other types of steel more susceptible to precision drilling, it would be easier to overhaul worn track shoes by re-drilling the pin bores of the hinge pin and could make it possible to use bearings in the bores to minimize the wear between the hinge pin and bore walls.